November, 2001

People who are born and bred in cities may be at increased risk of schizophrenia, researchers in Denmark report.

Their study found that individuals who spent their first 15 years of life in a highly urban area were nearly three times as likely to be diagnosed with schizophrenia, compared with people who grew up in rural areas. While a family history is the greatest risk factor for schizophrenia, people with no family history of the disease can also develop the disorder, indicating that environmental factors may play a role.

``In general, the more years lived in the higher the degree of urbanization, the greater the risk of schizophrenia,'' Drs. Carsten Bocker Pedersen and Preben Bo Mortensen from Aarhus University, Denmark, report in the November issue of the Archives of General Psychiatry.

The reasons for the associations are not clear but the authors suggest that complications at birth, diet, exposure to toxic materials, and infections may all contribute to risk. Some experts believe that certain infections during childhood make the developing brain more susceptible to schizophrenia.

Individuals who lived in urban areas at birth were more likely to be diagnosed with schizophrenia than those who lived in rural areas at birth. The risk rose in tandem with the number of years spent living in cities and with the degree of urbanization. Individuals who had moved to less urban areas between their 5th and 10th birthdays or between their 10th and 15th birthdays decreased their risk, the report indicates.

In other findings, a change of address during childhood that did not require a change of school had no effect on schizophrenia risk.

SOURCE: Archives of General Psychiatry 2001;58:1039-1046.